Applicant""s invention relates to a method of pretreating any component of a cementitious composition, particularly ash, that exhibits a high or highly varying adsorption characteristic, or both. The treatment method transforms the chemical adsorption characteristic of the component to a low constant value for use in processes that utilize the component. An important aspect of the present invention is that the method shifts the process of controlling the adsorption effects of the components from the end user to the component marketer.
The present invention relates to a method of treating a component or components of a cementitious composition that contains an appropriate surface morphology, such as that exhibited by unburned carbon or zeolite materials in fly ash, or both, for which the component exhibits the ability to adsorb chemicals from an aqueous solution.
The approach of the method is to satiate the adsorptive potential associated with the surface morphology by adding effective, trace amounts of a treatment agent or agents to the component(s) prior to addition of the component to the composition slurry. Thus, satiation of the adsorption potential occurs only after the treated component is placed in an aqueous solution. It is believed the addition to the aqueous solution (the composition slurry) enables mass transport of the intentionally added effective, trace amount of agent(s) to the adsorption sites.
Traditionally, the air entrainment quality of a cementitious composition has been controlled by the end user of the composition. Because of high or high variable adsorption characteristics, or both, the end user has the tedious task of adding the proper quantities of the various components of the cementitious composition. It is often by trial and error that a proper mix is achieved. There is a tremendous need for a way to control the consistency of the adsorption characteristics of mix components at the component supplier. There are numerous components of cementitious compositions which have varying adsorption potentials requiring control. These include ash, sand, cement aggregates, crushed stone, gravels, mortars, cements, clay, lime, lime sand, limestone, and various siliceous and aluminous materials.
While the discussion below focuses on fly ash as a component with high or highly variable adsorptive characteristics, it should be understood that any of the above identified components (and their equivalents) may be pretreated as discussed. The principles set forth are applicable to all of these components.
Ash is a byproduct of the combustion process. The major producer of ash in the United States is coal fired power plants, which generate on the order of 1xc3x97108 tons of fly and bottom ash annually.
A significant portion of the ash is pozzolanic in nature, which means that in the presence of moisture the ash will react with calcium hydroxide at ordinary temperatures to form compounds possessing cementitious properties. This pozzolanic nature of ash enables ash to be substituted for Portland cement in concrete in amounts up to 50%. While there are other uses for ash, the use of ash in concrete represents the single largest application that beneficially utilizes ash in a product. Unfortunately, however, the majority of ash that is generated at coal fired power plants is never utilized.
Federal clean air standards imposed upon coal burning power plants caused the power plants to reduce the combustion temperature in the boilers in order to reduce NOx emissions. The reduced combustion temperature causes a substantial increase in the amount of unburned carbon present in the ash. As a result of the thermal cycle, the unburned carbon in the ash exhibits some of the characteristics of a low-grade activated carbon, in particular, the ability to adsorb a wide range of chemicals. Traditionally ash with a high amount of unburned carbon is referred to as an ash with a high loss on ignition (LOI) content. LOI occurs when the ash is heated in the presence of air to temperatures that completely combust the unburned carbon to gaseous CO2 Ash with high LOI has traditionally been considered to be ash with high adsorption potential.
The adsorption potential of a high LOI ash is detrimental to the use of the ash as a Portland substitute in concrete due to the ash""s tendency to adsorb important cementitious chemical admixtures from the concrete during the mixing process rendering the admixtures unavailable to effect their intended purpose. Virtually all large scale commercial concrete applications require the use of cementitious admixtures for purposes such as entraining air for freeze-thaw protection, reducing water content for higher strength, and retarding or accelerating the initial set of the concrete.
However, it has been found that LOI is not a good indicator of ash adsorption potential. The specific amount of unburned carbon in the ash is a function of the specific combustion condition of the boiler when the coal is burned. Changing demands for electrical power result in changing combustion conditions which in turn results in varying amounts of unburned carbon in the ash. The variability associated with the amount of unburned carbon in the ash increases with increasing LOI. Thus, different loads of ash that are delivered to the concrete manufacturer will differ in LOI content and the amount of difference increases as the average LOI content increases. In addition, the changing combustion conditions influence the surface morphology of the unburned carbon, which directly influences the specific adsorption potential of the unburned carbon. Therefore, two different ash samples with the same LOI can exhibit radically different adsorption potentials. Furthermore, some combustion conditions can produce a surface morphology on the mineral phase of the ash that is capable of adsorption in a manner analogous to activated carbon. This zeolitic type of adsorption cannot be predicted based on the LOI of the ash.
The continuously varying adsorption potential of the ash (and all of the components to the cementitious composition) means that the admixture dosage necessary to compensate for the adsorption effect does not remain constant. The concrete industry, as a whole, is a low technology industry with low profit margins, and as such employs a trial and error method of determining the necessary compensatory admixture dosage. The combination of increased variability of the component adsorption potential with increasing LOI, low correlation between LOI and true adsorption potential of the component, and the trial and error method of determining the compensatory admixture dosage has resulted in enough off specification concrete to cause state regulatory bodies to lower the maximum ash LOI that is permitted to be used in concrete manufactured under their respective jurisdictions.
The concrete industry has responded to this problem by trying to develop admixtures that are both effective for their intended purpose and are not adsorbed by carbon. U.S. Pat. Nos. 4,453,978; 4,828,619; 5,110,362; and 5,654,352, teach and illustrate approaches to resolving this current problem. The methods have not been successful.
For example, the fundamental problem with developing admixtures that do not adsorb into the surface of carbon in ash is the wide range of surface morphologies that are produced on the carbon and mineral phases that are present in the ash by the differing combustion environments associated with the coal fired power plants.
U.S. Pat. No. 5,286,292 issued to Tsukada et al. introduced a new approach of satiating the adsorption potential of the ash before the ash is used. Their approach is to expose the ash to halogen gas (preferably fluorine or chlorine) which readily adsorbs onto the surface of the unburned carbon. Their preferred embodiment includes placing the ash into an enclosed vessel followed by the introduction of the fluorine and/or chlorine gas for a time period from 10 to 60 minutes. After this time, the prepared ash is usable as a Portland substitute without appreciable admixture adsorption by the unburned carbon in the ash.
Several problems have inhibited commercial implementation of Tsukata""s approach. Fluorine and chlorine gas are highly corrosive and are potentially lethal in relatively small doses to living organisms. Furthermore, the capital required to build a treatment facility from special corrosive resistant materials is high. In addition, the cost of the gas is high relative to the selling price of the ash. Additionally, changing environmental conditions can cause desorption of the gas from the unburned carbon in the ash thereby releasing this highly corrosive and potentially lethal gas into the atmosphere for possible exposure to both equipment and personnel downstream from the treatment facility.
The approach of the present invention is to provide a treatment and method for treating the ash without the problems of the known art. In the present invention, trace amounts of solid and/or liquid chemicals are added to the ash prior to the use of the ash in a subsequent process in order to mitigate the adsorption potential of the ash. Implementation of the approach of the present invention is well suited for either the ash generator or ash marketer because this approach results in greater product uniformity and eliminates the end user""s concern over the adsorption effect of the unburned carbon in the ash. Unlike Tsukata""s approach, the present invention does not satiate the unburned carbon during the treatment process, but rather the process enables the correct amount of chemicals to be present in the ash so as to satiate the adsorption effect when the ash is in an aqueous solution. Chemicals found to be useful for this purpose are members of the family of chemicals that strongly adsorb onto carbon and/or zeolitic substrates. Several highly effective chemicals have been identified that are not corrosive, not harmful to the environment, do not pose a health risk to personnel handling the ash, remain in the ash with changing environmental conditions, and are very inexpensive relative to the selling price of the ash. The exact treatment chemical used for a given ash is tailored for the specific surface chemistry and morphology of the subject ash.
An object of the present invention is to provide a novel treatment and method for treating any component or components of a cementitious composition that utilizes a treatment chemical or agent that is supplied to the component before the component is introduced into the utilizing process to control the apparent chemical adsorption potential of the component.
It is an object of the present invention to provide a novel treatment and method for treating any component(s) of a cementitious composition that lowers its adsorption potential, particularly for chemicals added during the utilizing process.
It is another object of the present invention to provide a novel treatment and method for treating any component(s) of a cementitious composition that controls its adsorption potential, particularly for chemicals added during the utilizing process.
Yet another object of the present invention is to provide a novel treatment and method for treating any component(s) of a cementitious composition that produces a component(s) with a consistent adsorption potential, particularly for chemicals added during the utilizing process.
Still another object of the present invention is to provide a novel treatment and method for treating any component(s) of a cementitious composition that controls the adsorption potential of component so as to easily accommodate the wide variety of surface morphologies and specific activities of both components from different sources and from a single source that changes with time.
It is yet another object of the present invention to provide a novel treatment and method for treating any component(s) of a cementitious composition that transforms ash into a useful raw material that the commercial market is willing and able to purchase and consume.
Another object of the present invention is to provide a novel treatment and method for treating ash that introduces the treatment chemical or chemicals into commercially xe2x80x9cbadxe2x80x9d ash simply, easily, and of low capital cost such that the total treatment cost of the ash is a very small fraction of the commercial selling price of the treated ash.
Still another object of the present invention is to provide a novel treatment and method for treating ash that does not pose an increased threat to the environment, to the health or safety of workers, or to equipment exposed to the treated ash relative to the untreated ash.
It is still another object of the present invention to provide a novel treatment and method for treating any component(s) of a cementitious composition that involves dispensing trace amounts of a treatment chemical or agents into the component before the component is used in any process.
Yet another object of the present invention is to provide a novel treatment and method for treating any component(s) of a cementitious composition that involves a treatment chemical or agents that works in combination with the utilizing process to produce the effect of controlling the apparent chemical adsorption potential of the component in that process.
It is another object of the present invention to provide a novel treatment and method for treating any component(s) of a cementitious composition that utilizes a treatment chemical or chemicals that strongly adsorbs onto carbon and/or zeolitic surfaces.
Still another object of the present invention is to provide a novel treatment and method for treating any component(s) of a cementitious composition that utilizes a treatment chemical or chemicals that does not have a detrimental effect on the utilizing process.
It is yet another object of the present invention to provide a novel treatment and method for treating any component(s) of a cementitious composition that utilizes a treatment chemical or chemicals that is a surfactant.
Yet another object of the present invention is to provide a novel treatment and method for treating any component(s) of a cementitious composition that utilizes a treatment chemical or chemicals that is a nonionic surfactant.
It is still another object of the present invention to provide a novel treatment and method for treating any component(s) of a cementitious composition that utilizes a treatment chemical or chemicals that is an ethoxylate.
Another object of the present invention is to provide a novel treatment and method for treating any component(s) of a cementitious composition that utilizes a treatment chemical or chemicals that is a nonylphenol ethoxylate.
It is another object of the present invention to provide a novel treatment and method for treating ash that utilizes a treatment chemical or chemicals in an amount in the range of about 0.001% to about 20.0% solid to solid, and, preferably, in the range of about 0.001% to about 2.0% solid to solid.
Yet another object of the present invention is to provide a novel treatment and method for treating any component(s) of a cementitious composition that utilizes a treatment chemical or chemicals that remains in the component or final product with changing environmental conditions.
It is another object of the present invention to provide a novel treatment and method for treating any component(s) of a cementitious composition that utilizes a treatment chemical or chemicals for the component that becomes effective when the component is placed in an aqueous solution.
Still another object of the present invention is to provide a novel treatment and method for treating any component(s) of a cementitious composition that utilizes a treatment chemical or chemicals that is an anionic surfactant.
Another object of the present invention is to provide a novel treatment and method for treating ash that utilizes a treatment chemical or chemicals that is sodium lauryl sulfate.
In satisfaction of these and related objectives, applicant""s present invention provides for a novel treatment and method for treating any component(s) of a cementitious composition that involves dispersing amounts (even trace amounts) of a treatment chemical or agents into the component before the component is used in a utilizing process. The treatment chemical or chemicals work in combination with the utilizing process to produce the effect of controlling the apparent chemical adsorption potential of the component in the utilizing process. At the initial step, a treatment chemical or chemicals is selected. Here, a subfamily of chemicals that beneficially interact with both the intended component and the utilizing process are selected from a family of chemicals that strongly adsorb onto carbon and/or zeolitic substrates. A subset of chemicals is next selected from the subfamily of chemicals which would not realistically increase the risk to the environment, workers"" health or safety, or integrity of equipment that is exposed to the treated component relative to the risks imposed by untreated component. Next, a candidate set of chemicals is selected from the subset of chemicals for which the cost of treatment is significantly below the commercial selling price of the treated component. Next, the necessary or effective amount of the treatment chemical or chemicals is determined and the treatment chemical or chemicals is prepared for introduction into the component. Last, the treatment chemical or chemicals is introduced into the component using one or more of batch mixing, combined flow, or other appropriate method or methods.